Chemical planar head dampening system

ABSTRACT

An improved polishing apparatus having a dampening system to prevent fluctuations between the planar head polishing device and the circuit panel. The dampening system includes a load actuation arm having a hydraulic-pneumatic cylinder which is controlled by an connected dampening circuit.

BACKGROUND OF THE INVENTION

[0001] 1. Technical Field

[0002] The present invention relates generally to the chemicalmechanical polishing of printed circuit boards, and more particularly,to a planar head dampening system for a chemical mechanical polishingsystem.

[0003] 2. Related Art

[0004] The strict process requirements of a chemical mechanicalpolishing system, used in the manufacture of printed circuit boards,necessitate the use of a compressible polishing device and theapplication of a low downward pressure, ranging from approximately 0.25to 10 psi. These requirements are essential to the polishing process dueto the delicate nature of the surface contours of the workpiece. Use ofa less compressible polishing device or attempting to increase the downpressure could eliminate these desired surface contours or otherwisedamage the workpiece. Unfortunately, gravity alone is insufficient tohold the polishing device in contact with the workpiece while polishing.Rather, in the absence of an applied down pressure, the polishing devicefloats above the workpiece without polishing its surface. Therefore, apolishing system utilizing a planar head polishing device having a lowdurometer compressible core in conjunction with the application of a lowdown pressure are currently used in the industry.

[0005] The requisite down pressure is typically supplied by a compressedair source. However, when the surface of the planar head polishingdevice was upgraded to a more aggressive material, a destructivephenomenon known as “high frequency cycling” was encountered. Highfrequency cycling results when the planar head is brought into contactwith the workpiece, and due to its coarse polishing surface, the planarhead begins to grip the surface of the workpiece and “bite-in.” Thiscauses the compressible inner core of the planar head to deform, forcingit in the opposite direction intended. Due to the compressible nature ofthe air providing the down pressure, the upward force exerted by thedeformed planar head produces a rebounding effect. These fluctuations incontact between the polishing device and the workpiece produceproportionate fluctuations in the planar head impression and the processrate of the workpiece. Additionally, premature failure of the planarhead lowering device, inconsistent surface conditions of the planar headand non-uniform planarization of the workpiece surface can result.

[0006] The high frequency cycling appears to be attributed to thecombination of the low durometer inner core of the planar head and thelow down pressure. In an attempt to remedy the problem, planar headscomposed of different durometer materials were tested. However, thesealternative materials created further processing problems and,therefore, offered no solution. In the alternative, various shockabsorbers were considered to eliminate the effects of the compressedair. However, none produced a regressive non-compressible system, whichwould allow the pressure to remain constant throughout polishing. Thesealternatives were also ineffective since they would be destroyed by theharsh chemical environment of the system.

[0007] Therefore, there is clearly a need to develop a chemicalmechanical polishing device which eliminates the occurrence of highfrequency cycling.

SUMMARY OF THE INVENTION

[0008] The present invention provides a device that will overcome theabove-identified problems through the use of a hydraulic-pneumaticdampening system.

[0009] A first general aspect of the present invention provides apolishing apparatus having at least one polishing device and a supportplatform comprising, a load actuating arm, mounted at a first end to thesupport platform and at a second end to the polishing device, and adampening circuit connected to the load actuating arm to preventfluctuations. This aspect allows for the application of a constant lowdown pressure of the polishing device, thereby eliminating theoccurrence of fluctuations between the planar head and the circuitpanel.

[0010] A second general aspect of the present invention includes apolishing apparatus comprising, a conveyor mounted to a platform totransport a workpiece to a polishing area of the apparatus, and a platepivotally secured above the conveyor carrying an at least one polishingdevice rotatably mounted therein. This aspect provides for the apparatusto transport a circuit panel to the polishing area of the apparatus andfor lowering the polishing device.

[0011] A third general aspect of the present invention includes apolishing apparatus having at least one polishing device and a supportplatform comprising, a conveyor mounted to the platform to transport acircuit panel to the at least one planar head assembly, a platepivotally secured above the conveyor, a planar head rotatably mountedwithin the plate, a load actuating arm, mounted at a first end to thesupport platform and at a second end to the plate, and a dampeningcircuit connected to the load actuating arm to prevent fluctuations.This aspect provides similar advantages to that of the first and secondaspects.

[0012] A fourth general aspect of the present invention includes apolishing apparatus having a dampening system to prevent fluctuations.This aspect provides similar advantages to that of the first and thirdaspects.

[0013] The foregoing and other features and advantages of the inventionwill be apparent from the following more particular description ofpreferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The preferred embodiments of this invention will be described indetail, with reference to the following figures, wherein likedesignations denote like elements, and wherein:

[0015]FIG. 1 depicts a cross-sectional view of the deformation of aplanar head upon contact with a workpiece, which necessitated thepresent invention;

[0016]FIG. 2 depicts a cross-sectional view of a chemical mechanicalpolishing assembly in accordance with the present invention;

[0017]FIG. 3 depicts a planar head in accordance with the presentinvention;

[0018]FIG. 4 depicts a cross-sectional view of a planar head inaccordance with the present invention;

[0019]FIG. 5 depicts a dampening circuit of the chemical mechanicalpolishing assembly in accordance with the present invention; and

[0020]FIG. 6 depicts a cross-sectional view of a hydraulic-pneumaticcylinder in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIDMENTS

[0021] Although certain preferred embodiments of the present inventionwill be shown and described in detail, it should be understood thatvarious changes and modifications may be made without departing from thescope of the appended claims. The scope of the present invention will inno way be limited to the number of constituting components, thematerials thereof, the shapes thereof, the relative arrangement thereof,etc., and are disclosed simply as an example of the preferredembodiments.

[0022]FIG. 1 shows a cross-sectional view of a deformation 6 of a planarhead 3 when brought into contact with a workpiece 2 carried on adelivery system 1, such as a conveyor, a robotic armature, a turn table,etc. While planar head 4 shows the ideal contact scenario, planar head 5depicts the deformation, illustrated by dashed line 6, that causesplanar head 5 to rebound away from workpiece 2, thereby producingnon-uniform planarization.

[0023]FIG. 2 depicts a cross-sectional view of a chemical mechanicalpolishing assembly 10, in accordance with the present invention. A backpanel 12 is attached perpendicularly to a platform 11. A conveyor 13, orother means of delivery, is mounted to back panel 12, and carries aworkpiece 14 to the various planar head assemblies A, B, etc., to bepolished. It should be appreciated that an infinite succession of planarhead assemblies may be used in accordance with the invention, and it isnot limited to number shown in the figures. A planar head 16, rotatablymounted about a solid shaft 28 within a plate 15, is propelled by apulley 17 via belts 19 and 20, which are powered by a motor 18. Itshould be recognized that chains, ropes, etc., could be used to propelplanar head 16. Further, motor 18 could be placed in alignment withplanar head 16, thereby eliminating the need for pulley 17. A loadactuation arm 21, designed to raise and lower plate 15 pivotally about apin P, is attached at one end to platform 11 via a bracket 24, in thisdepiction an L-shaped bracket is used, and at the other end to plate 15via a bracket 25. Load actuation arm 21 includes a hydraulic-pneumaticcylinder 26, fittings 22 and 23 located on both ends of cylinder 26, andan arm 27 slidably mounted within cylinder 26.

[0024]FIG. 5 shows a cross-sectional view of the dampening circuit whichcontrols the movement of load actuation arm 21. To lower planar head 16,a two position-four way valve 34 is placed in position 34 b. This allowscompressed air from supply 35 to apply pressure to a fluid reservoir 31,which supplies a chamber 35 of cylinder 26 (FIG. 6), with anon-compressible medium having a low viscosity, approximately 0.9 to 1.0centipoises. This draws arm 27 into cylinder 26 and lowers planar head16. A flow control area 33 includes a check valve 32 which permits thetransmission medium from fluid reservoir 31 to flow unrestricted in onedirection only, thereby preventing back flow and maintaining constantpressure in cylinder 26 during polishing. When polishing is complete,two position-four way valve 34 is switched to position 34 a, therebyredirecting compressed air from supply 35 into chamber 36 of cylinder 26(FIG. 6), and allowing chamber 36 to fill with compressed air and raiseplanar head 16. It should be appreciated that supply 35 is not limitedto the use of compressed air and may be replaced with other acceptablemediums, i.e., hydraulic fluid.

[0025]FIG. 3 depicts the configuration of planar head 16 having solidshaft 28. FIG. 4 shows a cross-sectional view of planar head 16, whichincludes solid shaft 28, an inner core 29 and an outer shell 30. Solidshaft 28 is preferably composed of titanium. Inner core 29 is preferablycomposed of a low durometer material, i.e., rubber. Outer shell 30 ispreferably a polishing paper material. In the alternative, outer shell30 may be composed of a higher durometer material than inner core 29 inconjunction with a polishing paper. However, these layers are notlimited to the use of these specific materials.

[0026] While this invention has been described in conjunction with thespecific embodiments outlined above, it is evident that manyalternatives, modifications and variations will be apparent to thoseskilled in the art. Accordingly, the preferred embodiments of theinvention as set forth above are intended to be illustrative, notlimiting. Various changes may be made without departing from the spiritans scope of the invention as defined in the following claims.

We claim:
 1. A polishing apparatus having at least one polishing deviceand a support platform comprising: a load actuating arm, mounted at afirst end to the support platform and at a second end to the polishingdevice; and a dampening circuit connected to the load actuating arm toprevent fluctuations.
 2. The polishing apparatus of claim 1 , whereinthe at least one polishing device is a planar head assembly.
 3. Thepolishing apparatus of claim 1 , wherein the load actuating arm is ahydraulic-pneumatic cylinder.
 4. The polishing apparatus of claim 1 ,wherein the dampening circuit further includes a two position-four wayvalve, which regulates the flow of air from a compressed air sourceleading to a fluid reservoir which supplies a transmission medium to theload actuating arm, a check valve and a flow control valve locatedbetween the fluid reservoir and the load actuating arm.
 5. The polishingapparatus of claim 4 , wherein the fluid reservoir contains anon-compressible medium having a viscosity of about 0.9 to 1.0centipoises.
 6. A polishing apparatus comprising: a conveyor mounted toa platform to transport a workpiece to a polishing area of theapparatus; and a plate pivotally secured above the conveyor carrying anat least one polishing device rotatably mounted therein.
 7. Thepolishing apparatus of claim 6 , wherein the at least one polishingdevice is a planar head assembly.
 8. The polishing apparatus of claim 6, further including a load actuating arm mounted at a first end to thesupport platform and at a second end to the plate and a dampeningcircuit connected thereto.
 9. The polishing apparatus of claim 8 ,wherein the load actuating arm is a hydraulic-pneumatic cylinder. 10.The polishing apparatus of claim 8 , wherein the dampening circuitfurther includes a two position-four way valve, which regulates the flowof air from a compressed air source leading to a fluid reservoir whichsupplies a transmission medium to the load actuating arm, a check valveand a flow control valve located between the fluid reservoir and theload actuating arm.
 11. The polishing apparatus of claim 10 , whereinthe fluid reservoir contains a non-compressible medium having aviscosity of about 0.9 to 1.0 centipoises.
 12. A polishing apparatushaving at least one polishing device and a support platform comprising:a conveyor mounted to the platform to transport a circuit panel to theat least one planar head assembly; a plate pivotally secured above theconveyor; a planar head rotatably mounted within the plate; a loadactuating arm, mounted at a first end to the support platform and at asecond end to the plate; and a dampening circuit connected to the loadactuating arm to prevent fluctuations.
 13. The polishing apparatus ofclaim 12 , wherein the at least one polishing device is a planar headassembly.
 14. The polishing apparatus of claim 13 , wherein the planarhead is composed of a solid shaft, an inner core and an outer shell. 15.The polishing apparatus of claim 14 , wherein the inner shaft istitanium.
 16. The polishing apparatus of claim 14 , wherein the innercore is a low durometer material.
 17. The polishing apparatus of claim14 , wherein the outer shell is a polishing paper material or a higherdurometer elastomer material than the inner core.
 18. The polishingapparatus of claim 12 , wherein the load actuating arm is ahydraulic-pneumatic cylinder.
 19. The polishing apparatus of claim 12 ,wherein the dampening circuit further includes a two position-four wayvalve, which regulates the flow of air from a compressed air sourceleading to a fluid reservoir which supplies a transmission medium to theload actuating arm, a check valve and a flow control valve locatedbetween the fluid reservoir and the load actuating arm.
 20. Thepolishing apparatus of claim 19 , wherein the fluid reservoir contains anon-compressible medium having a viscosity of about 0.9 to 1.0centipoises.
 21. A polishing apparatus having a dampening system toprevent fluctuations.
 22. The polishing apparatus of claim 21 , whereinthe dampening system further includes a load actuation arm and adampening circuit connected thereto.
 23. The polishing apparatus ofclaim 22 , wherein the load actuation arm is a hydraulic-pneumaticcylinder.
 24. The polishing apparatus of claim 22 , wherein thedampening circuit further includes a two position-four way valve, whichregulates the flow of air from a compressed air source leading to afluid reservoir which supplies a transmission medium to the loadactuating arm, a check valve and a flow control valve located betweenthe fluid reservoir and the load actuating arm.
 25. The polishingapparatus of claim 24 , wherein the fluid reservoir contains anon-compressible medium having a viscosity of about 0.9 to 1.0centipoises.